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What part of "it can't go through the engine bell walls" is causing you issues?

I know this one. I remember it from an old Stundie post that compared rockets to a can of silly string. The rocket doesn't actually push the exhaust out of the nozzle, so the walls don't matter. The vacuum instantly pulls the exhaust out of the rocket and into itself, so there's no thrust.

ETA: Found it.

Originally Posted by smartcooky

I submit this pearl of wisdom, from cluesforum.info

Thread: Why Rocketry Doesn't Work in the Vacuum

Poster: Vext Lynchpin

Date: June 18th, 2013, 8:00 pm

""I think the main point that the posters on this thread (who are more scientifically minded than I) have been making is that the vacuum itself exerts a force of its own that renders nil the force of the mass of gas escaping from a rocket's nozzle.

To use a simple analogy, think of a rocket and its escaping gas as an aerosol can full of silly string. When you press the button on the aerosol can, silly string is ejected at great speed. If there's enough speed, it may exert force on the aerosol can, so that the silly string is moving in one direction, and the can in the other. Newton.

But in a vacuum, the speed of the equalizing force of the vacuum is akin to someone pulling the silly string out of the aerosol can faster than it can be ejected, thus nullifying the force caused by the silly string's ejection.

Of course, the analogy isn't perfect, since pulling the silly string out would actually cause the aerosol can to move in the same direction as the pull. This wouldn't be a factor with gases being pulled into the vacuum."

It's not like you have to go to space to find a vacuum. This isn't some theoretical question we have to build a super collider the size of the moon to solve. This could be answered in any vacuum chamber here on Earth with Diet Coke and Mentos.

__________________- "Ernest Hemingway once wrote that the world is a fine place and worth fighting for. I agree with the second part." - Detective Sommerset
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It's not like you have to go to space to find a vacuum. This isn't some theoretical question we have to build a super collider the size of the moon to solve. This answered in any vacuum chamber here on Earth with Diet Coke and Mentos.

Exactly. But the video would have to be verifiably uneditable, which is tricky to prove. And if Gingervytes were actually there to witness the experiment he'd have to be in the chamber to check that it's really a vacuum. Looks like an irreducible delusion to me.

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It's not like you have to go to space to find a vacuum. This isn't some theoretical question we have to build a super collider the size of the moon to solve. This answered in any vacuum chamber here on Earth with Diet Coke and Mentos.

Any thrust would be the result of the exhaust pushing against the wall of the chamber, obviously.

The "NASA" rocket equation? I thought it was the Tsiolkovsky rocket equation.

Oh, I get it.... Tsiolkovsky was "in on it", a NASA shill, 62 years before NASA was even established.

I think "NASA" means he got that equation from NASA. Tsiolkovsky's equation is different and almost (but not entirely) unrelated. Tsiolkovsky's rocket equation is about total delta-V; thrust is merely implied because without thrust, the specific impulse would always be 0.

__________________"In times of war, we need warriors. But this isn't a war." - Phil Plaitt

I think "NASA" means he got that equation from NASA. Tsiolkovsky's equation is different and almost (but not entirely) unrelated. Tsiolkovsky's rocket equation is about total delta-V; thrust is merely implied because without thrust, the specific impulse would always be 0.

Oh, OK

I didn't bother reading his attachment. Its sideways, and I have a sore neck this morning.

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Maybe this should be moved to the Science section here, since that seem to be the place for crackpot science theories. I am not denying there is a conspiracy angle, but overall I think this should be dealt with as crackpot science.

__________________Pacifism is a shifty doctrine under which a man accepts the benefits of the social group without being willing to pay - and claims a halo for his dishonesty.

I think "NASA" means he got that equation from NASA. Tsiolkovsky's equation is different and almost (but not entirely) unrelated. Tsiolkovsky's rocket equation is about total delta-V; thrust is merely implied because without thrust, the specific impulse would always be 0.

Yes but it requires fuel mass turned into gas mass to achieve that delta v.

Yes but it requires fuel mass turned into gas mass to achieve that delta v.

Tsiolkovsky's rocket equation doesn't assume gas at all, merely that mass is ejected to create thrust (e.g. there's reaction mass). The Rocket Equation works just fine if, instead of thrusters, you have little slingshots firing mass slugs, or you're using a water rocket

__________________"In times of war, we need warriors. But this isn't a war." - Phil Plaitt

Tsiolkovsky's rocket equation doesn't assume gas at all, merely that mass is ejected to create thrust (e.g. there's reaction mass). The Rocket Equation works just fine if, instead of thrusters, you have little slingshots firing mass slugs, or you're using a water rocket

Well one good thing has come from this thread. I’ve obviously accepted that rockets work in space, but I’ve never taken the time to understand how. Now I have a much better understanding, so thanks to Jay and others.

__________________A fanatic is one who can't change his mind and won't change the subject.

"If NASA was willing to fake great accomplishments they'd have a second one by now." - xkcd.

__________________- "Ernest Hemingway once wrote that the world is a fine place and worth fighting for. I agree with the second part." - Detective Sommerset
- "Stupidity does not cancel out stupidity to yield genius. It breeds like a bucket-full of coked out hamsters." - The Oatmeal
- "To the best of my knowledge the only thing philosophy has ever proven is that Descartes could think." - SMBC

Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?

Because gravity and thrust aren't the same thing.

__________________- "Ernest Hemingway once wrote that the world is a fine place and worth fighting for. I agree with the second part." - Detective Sommerset
- "Stupidity does not cancel out stupidity to yield genius. It breeds like a bucket-full of coked out hamsters." - The Oatmeal
- "To the best of my knowledge the only thing philosophy has ever proven is that Descartes could think." - SMBC

Btw. the atmospheric pressure actually plays role. It lowers efficiency of rocket engine, as the speed through the nozzle depends on difference between pressures inside the engine and outside. If there was enough outside pressure, the gasses would just stay inside, and no work would be done.

Btw. the atmospheric pressure actually plays role. It lowers efficiency of rocket engine, as the speed through the nozzle depends on difference between pressures inside the engine and outside. If there was enough outside pressure, the gasses would just stay inside, and no work would be done.

Shill. Who's lining your pockets?

No seriously who. I want in.

__________________- "Ernest Hemingway once wrote that the world is a fine place and worth fighting for. I agree with the second part." - Detective Sommerset
- "Stupidity does not cancel out stupidity to yield genius. It breeds like a bucket-full of coked out hamsters." - The Oatmeal
- "To the best of my knowledge the only thing philosophy has ever proven is that Descartes could think." - SMBC

Don't do it. Don't get drug down into nitpicking the details when the core argument is fundamentally flawed.

He's trying to Jabba us.

__________________- "Ernest Hemingway once wrote that the world is a fine place and worth fighting for. I agree with the second part." - Detective Sommerset
- "Stupidity does not cancel out stupidity to yield genius. It breeds like a bucket-full of coked out hamsters." - The Oatmeal
- "To the best of my knowledge the only thing philosophy has ever proven is that Descartes could think." - SMBC

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maybe the problem is in your argument that perhaps you can not express clearly, dasmiller has great comprehension, perhaps you should try to actually explain your self in more than sound bytes.

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Is there pressure still pushing. Let us put an object on a scale and pick it up with a vacuum, why is there no opposite force on the scale?

Gravity isn't a sort of thrust.

The thing is, you can do these experiments of thrust yourself. There are places where they can damn near make vaccuums for you, and you can find some pressurised container, make a whole in it, and see it move.

So why are you wasting time on web forums rather than testing your idea?

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Nor is mechanical traction, although if you pull hard on something it will pull back. If instead of placing an object on a scale and pulling upward, you place a spring scale between an object and the hoist, the scale will register an increase in load as you begin to pull. This is inertial reaction, which combines with gravity to produce the scale reading. This is why crane operators take care not to lift speedily. The cable and tackle may well support the load's static weight, but not the additional dynamic force you might apply by starting and stopping the load abruptly.

Lifting something off a scale by drawing it upward into a vacuum immediately severs the coupling between the object and the scale. That much is obvious. However, put a giant scale underneath a rocket and measure the impingement force of its exhaust, and you will continue to get a reading as the rocket lifts off and stops weighing down the scale.

Quote:

So why are you wasting time on web forums rather than testing your idea?

Or collecting his Nobel prize in physics for having toppled Newton's laws of motion.

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